1,721,086 research outputs found
Optimal surrogate boundary selection and scalability studies for the shifted boundary method on octree meshes
No full textThe accurate and efficient simulation of Partial Differential Equations (PDEs) in and around arbitrarily defined geometries is critical for many application domains. Immersed boundary methods (IBMs) alleviate the usually laborious and time-consuming process of creating body-fitted meshes around complex geometry models (described by CAD or other representations, e.g., STL, point clouds), especially when high levels of mesh adaptivity are required. In this work, we advance the field of IBM in the context of the recently developed Shifted Boundary Method (SBM). In the SBM, the location where boundary conditions are enforced is shifted from the actual boundary of the immersed object to a nearby surrogate boundary, and boundary conditions are corrected utilizing Taylor expansions. This approach allows choosing surrogate boundaries that conform to a Cartesian mesh without losing accuracy or stability. Our contributions in this work are as follows: (a) we show that the SBM numerical error can be greatly reduced by an optimal choice of the surrogate boundary, (b) we mathematically prove the optimal convergence of the SBM for this optimal choice of the surrogate boundary, (c) we deploy the SBM on massively parallel octree meshes, including algorithmic advances to handle incomplete octrees, and (d) we showcase the applicability of these approaches with a wide variety of simulations involving complex shapes, sharp corners, and different topologies. Specific emphasis is given to Poisson's equation and the linear elasticity equations
Biomechanics simulations using cubic Hermite meshes with extraordinary nodes for isogeometric cardiac modeling
Full text linkCubic Hermite hexahedral finite element meshes have some well-known advantages over linear tetrahedral finite element meshes in biomechanical and anatomic modeling using isogeometric analysis. These include faster convergence rates as well as the ability to easily model rule-based anatomic features such as cardiac fiber directions. However, it is not possible to create closed complex objects with only regular nodes; these objects require the presence of extraordinary nodes (nodes with 3 or >= 5 adjacent elements in 2D) in the mesh. The presence of extraordinary nodes requires new constraints on the derivatives of adjacent elements to maintain continuity. We have developed a new method that uses an ensemble coordinate frame at the nodes and a local-to-global mapping to maintain continuity. In this paper, we make use of this mapping to create cubic Hermite models of the human ventricles and a four-chamber heart. We also extend the methods to the finite element equations to perform biomechanics simulations using these meshes. The new methods are validated using simple test models and applied to anatomically accurate ventricular meshes with valve annuli to simulate complete cardiac cycle simulations.This is a manuscript of the article Published as Krishnamurthy, Adarsh, Matthew J. Gonzales, Gregory Sturgeon, W. Paul Segars, and Andrew D. McCulloch. "Biomechanics simulations using cubic Hermite meshes with extraordinary nodes for isogeometric cardiac modeling." Computer aided geometric design 43 (2016): 27-38. doi:https://doi.org/10.1016/j.cagd.2016.02.016. Copyright 2016, The Authors. CC BY-NC-ND
Effects of the non-sinus-matching bioprosthetic aortic valve design on hemodynamics in the aorta
No full textTechnological advances in medical imaging and in-silico simulations of the cardiovascular system have informed our designs and medical procedures. Traditional numerical methods based on finite elements have been used to investigate various cardiovascular conditions. Isogeometric analysis (IGA) introduced new opportunities, such as reducing the number of parameters required to describe the geometry, higher order continuity of spline basis functions resulting in superior analysis fidelity, and avoiding tedious meshing of a computer-aided designed (CAD) object through the integration of CAD and analysis. The framework presented here has the following components:
1. Parameterized stented prosthetic valve design.
2. Parameterized aorta surface geometry.
3. Analysis-suitable trivariate non-uniform rational B-spline (NURBS) volumetric mesh.
4. Control over domain parameterization to ensure the quality of the analysis results.
5. IGA of all three domains of interest (i.e., solid, fluid, and thin shell structure).
6. Immersogeometric method, eliminating remeshing at the fluid and BHV interface.
We explain our framework and demonstrate its capabilities by analyzing the effects of surgical BHV replacement in axially asymmetric aortic roots on BHV’s performance and the changes in hemodynamics in the aorta as a case study. We look at the geometric orifice area, coaptation area, and maximum in-plane principal Green—Lagrange strain measurements quantitatively and the vortex formations qualitatively. This framework can ultimately be used to design better BHVs that match the sinus geometry, leading to better BHV performance and hemodynamic behavior
Effects of the non-sinus-matching bioprosthetic aortic valve design on hemodynamics in the aorta
No full textTechnological advances in medical imaging and in-silico simulations of the cardiovascular system have informed our designs and medical procedures. Traditional numerical methods based on finite elements have been used to investigate various cardiovascular conditions. Isogeometric analysis (IGA) introduced new opportunities, such as reducing the number of parameters required to describe the geometry, higher order continuity of spline basis functions resulting in superior analysis fidelity, and avoiding tedious meshing of a computer-aided designed (CAD) object through the integration of CAD and analysis. The framework presented here has the following components:
1. Parameterized stented prosthetic valve design.
2. Parameterized aorta surface geometry.
3. Analysis-suitable trivariate non-uniform rational B-spline (NURBS) volumetric mesh.
4. Control over domain parameterization to ensure the quality of the analysis results.
5. IGA of all three domains of interest (i.e., solid, fluid, and thin shell structure).
6. Immersogeometric method, eliminating remeshing at the fluid and BHV interface.
We explain our framework and demonstrate its capabilities by analyzing the effects of surgical BHV replacement in axially asymmetric aortic roots on BHV’s performance and the changes in hemodynamics in the aorta as a case study. We look at the geometric orifice area, coaptation area, and maximum in-plane principal Green—Lagrange strain measurements quantitatively and the vortex formations qualitatively. This framework can ultimately be used to design better BHVs that match the sinus geometry, leading to better BHV performance and hemodynamic behavior
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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